This invention relates generally to surveillance devices and photography, and more particularly to an image viewing device for producing and viewing high resolution fisheye images under various operational parameters and lighting conditions.
The camera is the basic instrument of photography. In its simplest form, a camera comprises a light-tight box with a lens at one end, which forms an image of the subject on light-sensitive film at the other end. A pinhole maybe substituted for the lens (e.g., a pinhole camera, camera obscura); however, this approach generally produces an image of the subject that is not sharp (i.e., poor resolution).
With reference to FIG. 1, there is shown a conventional camera 10, in accordance with the prior art. Nearly all modern cameras contain a glass or plastic lens or lens system 12 to focus a sharp image of the subject onto the film 14; a shutter 16 to control the length of time the film 14 is exposed, normally a fraction of a second; a viewfinder 18 to show the subject being photographed, and a mechanism (not shown) to hold the film and change film between exposures. A light-tight enclosure or housing 20 is also typically provided for protecting the film 14 from unintended exposure to the light. Many cameras include a lens aperture control (not shown) to regulate image brightness on the film. Advanced cameras may accept a variety of lenses for different photographic effects.
Cameras designed for still photography include, without limitation, the following types: box and other simple cameras, folding, 35-mm, reflex, press, view, instant picture, panoramic, electronic disk, underwater, aerial, stereo, medical, and document-copying or microfilm.
Cameras designed for action photography include, without limitation, the following types: videotape cameras, motion picture cameras, both conventional and high-speed, and television camerasxe2x80x94which are similar to photographic cameras but which use a light-sensitive electronic device instead of film.
Cameras have long been used for many purposes such as for surveillance, and especially covert surveillance. The availability of covert surveillance systems is of significant importance to certain groups, most especially the law enforcement and intelligence communities. The ability to detect and record images of subjects and events (especially those occurring in a interior portion of a room or a building) has permitted the gathering of evidence and information which had previously been difficult or impossible to do.
However, initial surveillance systems were unsatisfactory in that they did not permit the entire room to be viewed simultaneously. Typically, these surveillance systems employed a camera having a conventional lens systems wherein the field of view allowed the imaging of a relatively small area, typically a square or rectangular area directly in front of the camera. Therefore, events that occurred either below, above, or to the left or right of the field of view of a conventional camera escaped detection and recording by the surveillance system.
With reference to FIG. 2, there is shown a highly simplified conventional camera 22, in accordance with the prior art. In this view, only the lens 24, the film or image sensor 26, and the housing 28 are illustrated. As light rays L1, L2, L3, and L4 from an image enter the lens 24, they are focused and strike the image sensor 26 (e.g., film, semiconductor imager, etc.). It should be noted that only four light rays are shown in this view for ease of illustration. However, as previously noted, the main disadvantage of the conventional camera is that there is a limited field of view. As a result, only a relatively small portion of the total potential field of view can be viewed and recorded at any one given time.
In an effort to enlarge the field of view of surveillance systems, it was suggested that a camera having lens system capable of producing a 180xc2x0 field of view be employed. This 180xc2x0 field of view produces what is generally referred to as a xe2x80x9cfisheye view.xe2x80x9d The term xe2x80x9cfisheye viewxe2x80x9d refers to the fact that a fish sees a 180xc2x0 image of the external world above water which is folded into a relatively narrow cone when it views the water surface from below. A fisheye view may be produced by a conventional fisheye lens, which is typically a very wide angle lens. The conventional fisheye lens magnifies the parts of the image near the focal point (e.g., center of the image) and simultaneously de-magnifies parts of the image that are far away from the focal point. When using such a conventional fisheye lens, there is no practical way for an individual or object to enter the room without being observed and recorded. Several models of conventional fisheye lenses that achieve at least a 180xc2x0 field of view (including some that achieve a 220xc2x0 field of view) are readily commercially available from Nikon, Inc (Nikon Product Numbers 1405 NAS, 1402 NAS, and 1910 NAS).
However, conventional fisheye lenses are generally large and bulky devices that project several inches away from the face of the camera housing, making them extremely difficult to easily conceal. In order to overcome this problem, it was suggested that a conventional fisheye lens camera be placed or mounted behind a hole or an aperture in a wall or other suitable opaque object, thus concealing the camera completely. However, conventional fisheye lenses would need a relatively large aperture in order to allow for a sufficiently large enough angle, thus defeating the purposing of concealing the camera behind the wall. Therefore, conventional fisheye lens cameras are unsuitable for covert surveillance purposes where it is intended to place the camera behind a very small hole in a wall.
Therefore, there exists a need for an image viewing device that is easily concealable for covert surveillance uses but that is also capable of producing and viewing high resolution fisheye views under various operational parameters and lighting conditions.
In accordance with one embodiment of the present invention, an image viewing device comprises a member having an area defining an aperture, the light rays from the image entering through the aperture; and an optical block comprised of a refractive material, the optical block being located adjacent to the aperture, the optical block being capable of compressing the light rays from the image that pass through the aperture so as to produce an image comprising at least a 180xc2x0 field of view.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from the detailed description.